Question

Hi I am having the following problem. At the moment I am trying to create a bode plot for the following function.

G(s)=(Ks+3)/((s+2)(s+3))

Note: Not K(s+2)!

I then want to plot multiple bode plots for various values of K. Eg. 1,2,3, etc. I am having two separate issues.

1. How do I define the TF with a constant K in the location required (a multiple of s in the numerator)

2. How do I create multiple bode plots for values of K on the same plot?

Thanks

Answer 1

If you want to use K as variable you should go for manually plotting the bode instead of using built-in bode function.

w=0:1:100;
K=1;
Gs= ((K*1i*w)+3)./(((1i*w)+2).*((1i*w)+3));
subplot(211);
semilogx(w,20*log10(abs(Gs)));
ylabel('Magnitude in dB');
grid on;
title('K=1');

subplot(212);
semilogx(w,angle(Gs)*180/pi);
ylabel('Phase angle in degrees');
xlabel('frequency in rad/s');
grid on;

figure();
K=2;
Gs= ((K*1i*w)+3)./(((1i*w)+2).*((1i*w)+3));
subplot(211);
semilogx(w,20*log10(abs(Gs)));
ylabel('Magnitude in dB');
grid on;
title('K=3');

subplot(212);
semilogx(w,angle(Gs)*180/pi);
ylabel('Phase angle in degrees');
xlabel('frequency in rad/s');
grid on;

figure();
K=3;
Gs= ((K*1i*w)+3)./(((1i*w)+2).*((1i*w)+3));
subplot(211);
semilogx(w,20*log10(abs(Gs)));
ylabel('Magnitude in dB');
grid on;
title('K=3');

subplot(212);
semilogx(w,angle(Gs)*180/pi);
ylabel('Phase angle in degrees');
xlabel('frequency in rad/s');
grid on;